Method of depositing an electrically conductive oxide buffer layer on a textured substrate and articles formed therefrom

ABSTRACT

An article with an improved buffer layer architecture includes a substrate having a textured metal surface, and an electrically conductive lanthanum metal oxide epitaxial buffer layer on the surface of the substrate. The article can also include an epitaxial superconducting layer deposited on the epitaxial buffer layer. An epitaxial capping layer can be placed between the epitaxial buffer layer and the superconducting layer. A method for preparing an epitaxial article includes providing a substrate with a metal surface and depositing on the metal surface a lanthanum metal oxide epitaxial buffer layer. The method can further include depositing a superconducting layer on the epitaxial buffer layer, and depositing an epitaxial capping layer between the epitaxial buffer layer and the superconducting layer.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0001] The United States Government has rights in this inventionpursuant to Contract No. DE-AC05-000R22725 between the United StatesDepartment of Energy and UT-Battelle, LLC.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] (Not Applicable)

FIELD OF THE INVENTION

[0003] The invention relates generally to epitaxial metal oxide bufferlayers on metal substrates and articles made therefrom. Morespecifically, the invention relates to a process for depositingelectrically conductive oxide epitaxial layers on textured metalsubstrates, and articles made therefrom.

BACKGROUND OF THE INVENTION

[0004] Epitaxial metal oxide buffer layers on substrates withcrystalline, polycrystalline, or biaxially-textured metal surfaces arepotentially useful where an electronically active layer is deposited onthe buffer layer. The term “epitaxial” is used herein and understood bythose skilled in the art to mean the growth (method) and placement(apparatus) of a crystalline substance on a crystalline substrate, wherethe crystalline substance formed follows the crystallographicorientation of the crystalline substrate. Epitaxial crystal growthadvantageously permits the formation of crystallographic layers having ahigh level of crystallographic correlation with respect to an underlyingcrystalline substrate layer, permitting the formation of improveddevices.

[0005] The electronically active layer may be a superconductor, asemiconductor, a ferro-electric or an opto-electric material. Forexample, a biaxially-textured superconductor article to be used forpower transmission lines has a multi-layer composition 10, as in FIG. 1.Such deposited superconductor articles most commonly consist of abiaxially-textured metal surface 12, a plurality of buffer layers 14,16, and a superconducting layer 18. The biaxially-textured metal surface12, most commonly formed from Cu, Ag, Ni, or Ni alloys, provides supportfor the superconductor article, and can be fabricated over long lengthsand large areas.

[0006] Epitaxial metal oxide buffer layers 14, 16 comprise the nextlayers in the superconductor article. The buffer layers 14, 16 arecommonly formed from Y₂O₃ or CeO₂, and serve as chemical barriersbetween the metal surface 12 and the last layer, the last layer beingsuperconducting layer 18.

[0007] Current materials research aimed at fabricating improvedhigh-temperature superconductor articles is largely focused on epitaxialgrowth of high-temperature superconducting layers on biaxially-texturedmetal surfaces. A biaxially-textured article can be defined as apolycrystalline material in which the crystallographic in-plane andout-of-plane grain-to-grain misorientations are small (typically lessthan 20 degrees) but finite (typically greater than 2 degrees).Superconducting articles with current densities (J_(c)) in excess of 0.1MA/cm² at 77 K have been achieved for epitaxial YBa₂Cu₃O₇ films onbiaxially-textured Ni or Ni-based alloy surfaces with the use of certainepitaxial buffer layer constructs between the metal surface and thesuperconducting layer. In previous work, the synthesis ofhigh-temperature superconductor layers capable of carrying a high (atleast 0.1 MA/cm² at 77 K) J_(c) has required the use of complex,multilayered buffer architectures.

[0008] In order to realize a high-temperature superconducting layer,such as YBa₂Cu₃O₇, possessing a J_(c) greater than approximately 0.1MA/cm² at 77 K on a biaxially-textured metal substrate, the buffer layerarchitecture should be epitaxial relative to the metal substrate andcrack-free. Most preferably, the grains of the buffer layer should becrystallographically aligned perpendicular to the plane of the metalsubstrate (c-axis oriented) and parallel to the plane of the metalsubstrate (a-b alignment). Formation of superconductor articles withthis orientation begins with the selection of the metal surface 12. Thecrystallographic orientation of the metal surface 12 is preferablymaintained in the buffer layers 14, 16 and the superconducting layer 18,to the maximum extent possible. Numerous conventional processes arecurrently being used to grow buffer layers 14, 16 on a metal substrate12. These processes include vacuum methods, such as pulsed laserdeposition, physical vapor deposition electron beam evaporation andsputtering. Also, non-vacuum deposition processes, such as chemicalsolution deposition and chemical vapor deposition can be used for thispurpose.

[0009] In addition to being epitaxial relative to the biaxially-texturedmetal surface, buffer layers 14, 16 are preferably chemically compatiblewith both the metal surface and superconductor, and mechanically robustso as to prevent microscopic crack formation in the high-temperaturesuperconducting layer and the buffer layers. Prior to the presentinvention, buffer layers that met these objectives have requiredmultilayer combinations of various oxides.

[0010] For example, CeO₂ has been used to nucleate an epitaxial (001)oriented oxide layer on a biaxially textured (100) Ni surface. However,CeO₂ films of over 100 nm thickness form cracks on {100}<001 > texturedNi substrates due to significant differences in the thermal expansioncoefficients of the oxide film and the Ni substrate. Cracking hasprevented utilization of CeO₂ as a single buffer layer.

[0011] Also, YBCO films grown directly on a YSZ buffer layer on Nisubstrates result in two in-plane orientations. This is due to thelattice mismatch between YBCO and YSZ layers. This generally preventsuse of YSZ as a single buffer layer.

[0012] An additional buffer layer, such as an epitaxialyttria-stabilized zirconia (YSZ) buffer layer on a CeO₂ buffer layer hasbeen used to achieve substantially crack-free superconductor articles.The architecture of YBCO/CeO₂/YSZ/CeO₂/Ni has been the standardarchitecture for the rolling-assisted biaxially textured substrate(RABiTS) based YBCO coated conductors. In this arrangement, the superiormechanical properties of the YSZ layer substantially circumvent themicrocracking problem, and enable the formation of superconductinglayers with a high J_(c). The CeO₂ layer serves primarily to nucleate a(001) oriented epitaxial oxide on the metal surface.

[0013] An alternative multi-layer buffer layer uses conducting SRO(SrRuO₃ or Sr₂RuO₄) and LNO (LaNiO₃) buffer layers to formYBCO/SRO/LNO/Ni. The suppression of superconducting criticaltemperatures (T_(c)) of 75-80 K for YBCO films grown directly on LNObuffers has prevented the use of LNO as the single buffer layer. Also,the preparation of both SRO and LNO target materials are extremelydifficult.

[0014] Though effective in forming a high J_(c) superconductor article,the use of a multilayer buffer architecture, as opposed to a singlelayer buffer architecture, increases the complexity of thesuperconductor article fabrication process. Using multiple buffer layerstypically requires the use of additional raw materials, as compared to asingle buffer layer architecture. In addition, having CeO₂ as thenucleating layer tends to permit the formation of microscopic cracksthat can limit the maximum J_(c) of the superconductor article or resultin reliability problems during field use.

[0015] Epitaxial metal oxides on crystalline or polycrystalline metalsurfaces have potential application in fields other thansuperconductors. Epitaxial metal oxides on crystalline metal surfacesmay prove useful where thin epitaxial layers are needed in electronicapplications. Furthermore, epitaxial oxide layers on polycrystallinemetal surfaces have potential use in tribological or fuel cellapplications where the properties of the metal/oxide interface largelydetermine material performance. For epitaxy on randomly-orientedpolycrystalline metal surfaces, the epitaxial relationship involves agrain-by-grain registry of film and substrate crystallographicorientations.

SUMMARY

[0016] An epitaxial article includes a substrate having a textured metalsurface, a single lanthanum metal oxide epitaxial buffer layer disposedon and in contact with a surface of the substrate, and anelectromagnetically active layer disposed on and in contact with thesingle epitaxial buffer layer. The lanthanum metal oxide epitaxialbuffer layer can be selected from compounds having the general formulaLa_(1-x)A_(x)MO₃, where A and M are metals and 0≦x≦0.8. A can be Sr, Baor Ca, while M can be Mn or Co. The buffer layer can have a resistivityof less than 1 mOhm-cm at 300 K, or more preferably less than 0.1mOhm-cm.

[0017] The electromagnetically active layer preferably includes asuperconducting layer, the superconductor layer being an oxidesuperconductor. The oxide superconductor layer can be REBa₂Cu₃O₇ whereRE is a rare earth element, Tl₁Ba₂Ca_(n−1)Cu_(n)O_(2n+3), where n is aninteger between 1 and 4, Tl₂Ba₂Ca_(n−1)Cu_(n)O_(2n+4) where n is aninteger between 1 and 4, or Hg₁Ba₂Ca_(n−1)Cu_(n)O_(2n+2), where n is aninteger between 1 and 4.

[0018] The textured substrate can be a rolled and annealedbiaxially-textured metal substrate. The textured metal surface can be ametal selected from Cu, Cu-based alloys, Co, Mo, Cd, Pd, Pt, Ag, Al, Ni,and Ni-based alloys. Alternatively, the textured metal surface can be ametal selected from Ni or Ni-based alloys with at least one alloyingagent selected from Co, Cr, V, Mo, W, and rare earth elements.

[0019] In an alternate embodiment of the invention, an epitaxial articleincludes a substrate having a textured metal surface, a lanthanum metaloxide epitaxial buffer layer disposed on and in contact with a surfaceof the substrate, and at least one epitaxial capping layer disposed onand in contact with the lanthanum metal oxide epitaxial buffer layer.The epitaxial capping layer is a different composition compared to thebuffer layer. An electromagnetically active layer is disposed on and incontact with the epitaxial capping layer.

[0020] The epitaxial buffer layer can be selected from compounds havingthe general formula La_(1-x)A_(x)MO₃, where A and M are metals and0≦x≦0.8. A can be Sr, Ba or Ca and M can be Mn or Co.

[0021] The electromagnetically active layer can include asuperconducting layer.

[0022] Preferably, the superconductor layer is an oxide superconductor.The oxide superconductor can be REBa₂Cu₃O₇, where RE is a rare earthelement, Tl₁Ba₂Ca_(n−1)Cu_(n)O_(2n+3), where n is an integer between 1and 4, Tl₂Ba₂Ca_(n−1)Cu_(n)O_(2n+4), where n is an integer between 1 and4, or Hg₁Ba₂Ca_(n−1)Cu_(n)O_(2n+2), where n is an integer between 1 and4.

[0023] The substrate can be a rolled and annealed biaxially-texturedmetal substrate.

[0024] The metal textured surface can be a Cu, Cu-based alloy, Co, Mo,Cd, Pd, Pt, Ag, Al Ni, or a Ni-based alloy. The textured surface can beNi or a Ni-based alloy with at least one alloying agent selected fromCo, Cr, V, Mo, W, and rare earth elements.

[0025] The epitaxial capping layer can be a rare earth oxide. Thecapping layer can be SRO, LNO, YSZ, CeO₂ or Y₂O₃.

[0026] A method for preparing an epitaxial article, includes the stepsof providing a substrate with a textured metal surface, depositing asingle lanthanum metal oxide epitaxial buffer layer on and in contactwith the surface of the substrate, and depositing an electromagneticallyactive layer on the single lanthanum metal oxide epitaxial buffer layer.Preferably, the substrate provides a biaxially-textured metal surface.The method can include the step of rolling and annealing a metalmaterial to form a biaxially-textured substrate surface. Preferably, themetal rolled and annealed is Cu, Cu-based alloy, Co, Mo, Cd, Pd, Pt, Ag,Al, Ni, or a Ni-based alloy.

[0027] If a Ni-based alloy is used, an alloying agent such as Co, Cr, V,Mo, W, and rare earth elements is preferably added.

[0028] The lanthanum metal oxide epitaxial buffer layer can have thegeneral formula La_(1-x)A_(x)MO₃, where A and M are metals and 0≦x≦0.8.A can be Sr, Ba or Ca, while M can be Mn or Co. The lanthanum metaloxide epitaxial buffer layer can have a resistivity at 300 K of lessthan 1 mOhm-cm, or more preferably, less than 0.1 mOhm-cm.

[0029] The electromagnetically active layer can include asuperconducting layer. The superconductor layer is preferably an oxidesuperconductor, the oxide superconductor layer being REBa₂Cu₃O₇, whereRE is a rare earth element, Tl₁Ba₂Ca_(n−1)Cu_(n)O_(2n+3), where n is aninteger between 1 and 4, Tl₂Ba₂Ca_(n−1)Cu_(n)O_(2n+4), where n is aninteger between 1 and 4, or Hg₁Ba₂Ca_(n−1)Cu_(n)O_(2n+2), where n is aninteger between 1 and 4.

[0030] The lanthanum metal oxide epitaxial buffer layer is preferablydeposited by a sputtering process. The sputtering process can berf-magnetron sputtering. The electromagnetically active layer can bedeposited by a process of pulsed laser ablation, physical vapordeposition such as electron beam evaporation and sputtering, solutiondeposition and chemical vapor deposition.

[0031] A method for preparing an epitaxial article includes the steps ofproviding a substrate with a textured metal surface, depositing a singlelanthanum metal oxide epitaxial buffer layer on the surface of thesubstrate, and depositing at least one epitaxial capping layer on thesingle lanthanum metal oxide epitaxial buffer layer. The epitaxialcapping layer is of a different composition than the single lanthanummetal oxide epitaxial buffer layer. An electromagnetically active layeris deposited on the epitaxial capping layer. The method can include thestep of providing a biaxially-textured metal surface, preferably byrolling and annealing a metal material to form the biaxially-texturedsubstrate. A metal substrate is preferably a Cu, Cu-based alloy, Co, Mo,Cd, Pd, Pt, Ag, Al, Ni, or Ni-based alloy. If a Ni-based alloy is used,alloying agents are preferably Co, Cr, V, Mo, W, or rare earth elements.

[0032] The Lanthanum metal oxide epitaxial buffer layer can be acompound having the general formula La_(1-x)A_(x)MO₃, where A and M aremetals and 0≦x≦0.8. A can be Sr, Ba and Ca. M can be Mn or Co.

[0033] The electromagnetically active layer can include asuperconducting layer, preferably an oxide superconductor. The oxidesuperconductor can be REBa₂Cu₃O₇, where RE is a rare earth element,Tl₁Ba₂Ca_(n−1)Cu_(n)O_(2n+3), where n is an integer between 1 and 4,Tl₂Ba₂Ca_(n−1)Cu_(n)O_(2n+4), where n is an integer between 1 and 4 orHg₁Ba₂Ca_(n−1)Cu_(n)O_(2n+2), where n is an integer between 1 and 4.

[0034] The lanthanum metal oxide epitaxial buffer layer can be depositedby a sputtering process. The sputtering process is preferably anrf-magnetron sputtering process. The electromagnetically active layer ispreferably deposited by a pulsed laser ablation process. The epitaxialcapping layer can be SRO, LNO, YSZ, CeO₂,Y₂O₃ or a rare earth oxide.

[0035] An epitaxial article can provide a foundation for applyingelectromagnetically active layers directly thereon, and include asubstrate having a textured metal surface, and a single lanthanum metaloxide epitaxial buffer layer disposed on and in contact with the surfaceof the substrate. No additional buffer layer is required with thisarchitecture. The lanthanum metal oxide epitaxial buffer layer can be acompound having the general formula La_(1-x)A_(x)MO₃, where A and M aremetals and 0≦x≦0.8. A can be Sr, Ba or Ca. M can be Mn or Co.

[0036] A method for preparing an epitaxial article for applyingelectromagnetically active layers directly thereon includes the steps ofproviding a substrate with a textured metal surface and depositing asingle lanthanum metal oxide epitaxial layer on the substrate. The metalsurface is a preferably a biaxially-textured metal surface, formed byrolling and annealing a metal material. Metals such as Cu, Cu-basedalloys, Ag, Al, Co, Mo, Cd, Pd, Pt, Ni, or Ni-based alloys arepreferably rolled and annealed. If a Ni-based alloy is used, alloyingagents are preferably Co, Cr, V, Mo, W, or rare earth elements.

[0037] The lanthanum metal oxide epitaxial layer can be a compoundhaving the general formula La_(1-x)A_(x)MO₃, where A and M are metalsand 0≦x≦0.8. The lanthanum metal oxide epitaxial layer can be depositedusing a sputtering process. Preferably, the sputtering is rf-magnetronsputtering.

[0038] An epitaxial article includes a substrate having a metal surface,a single electrically conductive epitaxial buffer layer, and anelectromagnetically active layer disposed on and in contact with thesingle epitaxial buffer layer, the buffer layer being substantiallycrack-free. The epitaxial buffer layer can be at least 100 nm thickwithout substantially cracking. The epitaxial buffer layer can have aresistivity at 300 K of less than 1 mOhm-cm, or more preferably lessthan 0.1 mOhm-cm. In the preferred embodiment, the electromagneticallyactive layer includes a superconducting layer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] There are shown in the drawings embodiments which are presentlypreferred, it being understood, however, that the invention is notlimited to the precise arrangements and instrumentalities shown,wherein:

[0040]FIG. 1 is a cross-sectional view of a superconductor articlehaving a multilayer buffer composition.

[0041]FIG. 2 illustrates a schematic diagram showing some examplesuperconductor layer architectures using textured-Ni or Ni-alloysubstrates. FIG. 3 illustrates a typical θ-2θ scan for a 600 nm thickLSMO (La_(1-x)Sr_(x)MnO₃ where x=0.3) film on {100}<001 > Ni—W (3%)substrates.

[0042]FIG. 4 illustrates a typical 0-20 scan for a 600 nm thick LSMOfilm on {100}<001 > Ni substrates.

[0043]FIG. 5 illustrates a LSMO (111) pole figure for LSMO films growndirectly on textured-Ni substrates by rf magnetron sputtering.

[0044]FIG. 6 illustrates the SEM surface morphology of 600 nm thick LSMOfilm on textured-Ni substrates.

[0045]FIG. 7 illustrates Rutherford backscattering spectra from a 600 nmthick LSMO film on textured-Ni substrate.

[0046]FIG. 8 illustrates the temperature dependence of resistivity forpure Ni, LSMO film on Ni, and YBCO/LSMO/Ni substrates.

[0047]FIG. 9 illustrates Omega (ω) and Phi (φ) scans for a 190 nm thickpulsed laser deposition (PLD) YBCO film on 600 nm thick sputteredLSMO/Ni substrates.

[0048]FIG. 10 illustrates a YBCO (113) pole figure for a 190 nm thickPLD YBCO film on 600 nm thick sputtered LSMO/Ni substrate.

[0049]FIG. 11 illustrates the field dependence of critical currentdensity, J_(c), for a 190 nm thick PLD YBCO film on 600 nm thicksputtered LSMO/Ni substrates.

[0050]FIG. 12 illustrates a typical θ-2θ scan for a 300 nm thick LMO(LaMnO₃) film on {100}<001 > Ni substrates.

[0051]FIG. 13 illustrates a typical θ-2θ scan for a 300 nm thick LMOfilm on {100}<001 > Ni—W (3%) substrates.

[0052]FIG. 14 illustrates a LMO (111) pole figure for a 300 nm thicksputtered LMO/Ni substrate.

[0053]FIG. 15 illustrates Omega (ω) and Phi (φ) scans for a 200 nm thickpulsed laser deposition (PLD) YBCO film on a 300 nm thick sputteredLMO/Ni substrate.

[0054]FIG. 16 illustrates the temperature dependence of resistivity fora 200 nm thick PLD YBCO film on a 300 nm thick sputtered LMO/Nisubstrate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0055] The invention relates to an epitaxial article comprising anepitaxial lanthanum metal oxide buffer layer on a substrate having atextured metal surface. The preferred lanthanum metal oxide buffer layeris lanthanum strontium manganate, La_(1-x)Sr_(x)MnO₃, where 0≦x≦0.8(LSMO). A preferred embodiment relates to a biaxially-texturedsuperconductor article comprising an epitaxial lanthanum metal oxidebuffer layer (001) layer grown on a biaxially-textured metal surface,and a method of fabricating this article.

[0056] A high-temperature superconducting layer can be depositeddirectly on the epitaxial lanthanum metal oxide buffer layer to resultin the architecture YBa₂Cu₃O₇(YBCO)/LSMO/Ni. In such an arrangement, thearticle has a single buffer layer architecture that can yield asuperconducting layer with a J_(c) of at least 0.1 MA/cm² at 77 K.Preferably, the superconducting layer has a J_(c) of at least 0.5 MA/cm²at 77 K. For YBCO coated conductors, the architecture provides improvedreliability over previous superconducting architectures.

[0057] A related embodiment consists of the same lanthanum metal oxideepitaxial buffer layer on a metal substrate structure with an additionalthin oxide capping layer between the lanthanum metal oxide epitaxialbuffer layer and the electromagnetically active layer, such as asuperconducting layer. This capping layer can be significantly thinnerthan a typical buffer layer in that it can be as thin as a single unitcell. Preferably, however, the capping layer is between 10 nm and 40 nmthick. The capping layer can help alleviate the lattice mismatch whichcan exist between the epitaxial buffer layer and the superconductinglayer, and can improve the crystallinity and resulting performance ofthe superconducting article.

[0058] The superconductor article having a capping layer can have aJ_(c) of at least 0.2 MA/cm² at 77 K. Preferably, a superconductorarticle according to this embodiment can have a critical J_(c) of atleast 1.0 MA/cm² at 77 K.

[0059] Articles according to the invention can be used with anyelectronic application in which epitaxy and/or crystallographic textureis important, and are, specifically useful in forming high-temperaturesuperconductor articles, such as superconducting wires or tapes.Although particularly well suited for use in devices which includesuperconducting layers, articles formed using the invention are useful,in certain instances in conjunction with one or more additional layers,in applications including a wide variety of electromagnetic applicationswhich require electromagnetically active layers. For example, improvedpiezo-electrics, photovoltaics, tribological or fuel cells can beproduced using the invention. In addition, lanthanum metal oxidebuffered metal substrates may be useful for GMR (Giant MagnetoResistance), ferro-electric devices, electro-optic devices and forcatalytic properties.

[0060] A biaxially-textured substrate preferably used with the inventioncan be fabricated by scalable rolling and annealing techniques. Thesubstrate can then be reacted by a variety of techniques to produce achemically compatible, textured substrate. An epitaxial layer of anothermaterial can then be grown onto the textured substrate. This epitaxiallayer can be a buffer layer or a conducting layer, although it ispreferably a buffer layer. The texture of the substrate can be inducedin the epitaxial layer. Thus, it is possible to deposit abiaxially-textured superconductor with a high J_(c) using amechanically-robust epitaxial lanthanum metal oxide epitaxial bufferlayer directly in contact with the metal substrate surface.

[0061] A biaxially-textured article can be defined as a polycrystallinematerial in which the crystallographic in-plane and out-of-planegrain-to-grain misorientations are small (typically less than 20degrees) but finite (typically greater than 2 degrees). The degree ofbiaxial texture can be described by specifying the distribution of grainin-plane and out-of-plane orientations as determined by x-raydiffraction. Using x-ray diffraction data, full-width-half-maximum(FWHM) data of the out-of-plane (Δω) and in-plane (Δφ) reflections canbe determined. Therefore, the degree of biaxial texture for a givensample can be defined by specifying the range of Δω and Δφ for a givensample.

[0062] It is known that the J_(c) of an oxide superconductor may bereduced significantly if misorientation angles between individual grainsin the grain boundaries between grains are generally greater thanapproximately 5 to 10 degrees. Although some useful superconductorarticles may still be formed using substrates with larger grainmisorientations, it is usually desirable to obtain superconductinglayers in which the number of grain boundaries with misorientationangles greater than approximately 5 to 10 degrees is minimized.Similarly, for superconductor articles in which the superconductingdeposit is epitaxial with an underlying metallic or oxide buffer layeror substrate, it is desirable to minimize the number of grain boundarieswith misorientations greater than approximately 5 to 10 degrees.

[0063] The metal surface can be any metal upon which a lanthanum metaloxide buffer layer may be grown. However, the metal layer is preferablyat least uni-axial textured for most applications. For example, GMRdevices and piezo-electrics can utilize uni-axis textured substrates.However, applied to superconducting articles, the metal surface is mostpreferably biaxially-textured.

[0064] As discussed above, the buffer layer may be formed from a varietyof materials. The lanthanum metal oxide epitaxial buffer layer can beselected from compounds having the general formula La_(1-x)A_(x)MO₃,where A and M are metals and 0≦x≦0.8. A can be at least one metalselected from Group IIa metals including Sr, Ba and Ca. M can beselected from the group of transitional metals, preferably selected fromeither Mn or Co. The buffer layer may also be formed from LaMnO₃ (LMO).

[0065] The lanthanum metal oxide buffer layer is substantiallyelectrically conductive, as opposed to previous insulating buffer layerssuch as CeO₂ and YSZ. For example, LSMO layers are metallic with roomtemperature resistivity of around 1 mOhm-cm. Applied to superconductingarticles, an electrically conductive buffer layer is highly advantageousas it can significantly enhance the field reliability of asuperconductor article. Preferably the room temperature (300 K)resistivity of the lanthanum metal oxide buffer layer is less than 1mOhm-cm. Most preferably, the room temperature resistivity is less than0.1 mOhm-cm.

[0066] Assuming the superconductor article is used to carry highelectrical currents, if superconducting properties are lost, even duringa short period of time, destruction of the superconducting article fromoverheating can result. For example, a superconducting article loses itssuperconducting above the cutoff temperature, typically around 90 K. Ifthe temperature rises above the cutoff temperature, and there is noconductive path in the superconducting article to shunt the current, thesuperconductor article can be damaged or destroyed, due to dissipationof excessive power through the superconductor layer. In addition, whenapplied to electrical power transmission lines, lightening can result incurrent surges which can damage or destroy the superconducting article.

[0067] Using an electrically buffer layer, such as conductive lanthanummetal oxide buffer layer to support a superconducting layer results inthe formation of an electrical shunt to the metal substrate which canprotect the superconductor layer. During periods the superconductorcould be otherwise be damaged or destroyed due to excessive powerdissipation, the lanthanum metal oxide buffer layer can direct currentaway from the superconducting layer to the metal substrate.

[0068] In addition, the electrically conductive lanthanum metal oxidebuffer layer can permit operation of a superconducting article ratherthan failure, even if microcracks develop in the superconducting layerduring field use of the superconductor. In the case of microcracks inthe superconducting layer, current can bypass the micro-crack region andbe substantially conducted by the parallel combination of the lanthanummetal oxide buffer layer and metal substrate, bypassing the microcrackregions.

[0069] After formation of the buffer layer, a superconducting layer canbe deposited on the exposed buffer layer by a variety of techniques thatare well known in the art, such as physical vapor deposition includingpulsed laser deposition, electron beam evaporation and sputtering,solution deposition and chemical vapor deposition. The superconductinglayer can comprise any high-temperature superconducting materials,including REBa₂Cu₃O₇, where RE is a rare earth element.

[0070] A biaxially-textured, high critical J_(c) superconducting articlehaving a (001) oriented epitaxial lanthanum metal oxide buffer layer canbe formed by the additional step of growing an epitaxial superconductinglayer on the (001) lanthanum metal oxide buffer surface.

[0071] For example, high temperature superconductors such as REBa₂Cu₃O₇,Tl₁Ba₂Ca¹⁻¹Cu_(n)O_(2n+3), Tl₂Ba₂Ca_(n−1)Cu_(n)O_(2n+4), andHg₁Ba₂Ca_(n−1)Cu_(n)O_(2n+2) where n is an integer between 1 and 4 canbe disposed on the lanthanum metal oxide buffer layer. Other hightemperature superconductors which are chemically and epitaxiallycompatible can also be used with the invention.

[0072] In-plane variants superconducting layers, such as a REBa₂Cu₃O₇layer, rotated by 45°, can be present, due to the lattice mismatchbetween the superconductor layer and the buffer layer. Minimizing oreliminating one of the in-plane variants by optimization of growthtemperature and oxygen partial pressure can lead to a significantincrease in the critical J_(c). A more manufacturable approach toeliminating one of these in-plane variants is to deposit a thin,epitaxial capping layer of SRO (SrRuO₃ or Sr₂RuO₄), LNO (LaNiO₃), YSZ,CeO₂, Y₂O₃, or RE (rare earth) oxides, such as RE₂O₃ and RE₂Zr₂O₇. Usinga lanthanum metal oxide buffer layer such as LSMO as the first bufferlayer, examples of some useful architectures include YBCO/SRO/LSMO/Ni,YBCO/LNO/LSMO/Ni, YBCO/CeO₂/LSMO/Ni, YBCO/CeO₂/YSZ/LSMO/Ni,YBCO/RE₂O₃/LSMO/Ni, and YBCO/RE₂Zr₂O₇/LSMO/Ni. Depositing at least oneappropriate capping layer on the lanthanum metal oxide buffer layer canimprove the lattice match with the YBa₂Cu₃O₇ superconducting layer.Capping layers can be deposited using any suitable deposition method,including any of the deposition methods identified above.

[0073] Capping layers can be deposited at a temperature of betweenapproximately 25° C. and approximately 900° C., and is preferablydeposited at a temperature of between approximately 400° C. andapproximately 850° C. The oxygen partial pressure during capping layerdeposition should be between approximately 1×10⁻¹¹ Torr andapproximately 2×10⁻¹ Torr, and is preferably between approximately1×10⁻⁵ Torr and approximately 1×10⁻³ Torr. The capping layer can be asthin as a single unit cell, although the optimal thickness is between 10nm and 40 nm.

[0074] Incorporating this capping layer into the above-discussed singlebuffer layer architecture results in a relatively simplebiaxially-textured superconducting article with a J_(c) greater than 0.2MA/cm² at 77 K, and preferably at least 1.4 MA/cm² at 77 K.

[0075] A method for forming a high-temperature superconductor with asingle buffer layer architecture includes a pretreatment of the metalsubstrate having a surface, followed by growth of a lanthanum metaloxide buffer layer on the surface of the metal substrate. The processbegins with the formation of the metal surface. If a biaxially-texturedmetal surface is desired, a preferred approach is to form abiaxially-textured metal substrate by rolling and annealing. During therolling process, plastic flow causes reorientation of the lattice of theindividual grains of a polycrystalline material. As a result, thepolycrystalline material tends to gradually develop a texture orpreferred orientation of the lattice in the grains. The orientationchange proceeds as plastic flow continues, until a texture is reachedthat is stable against indefinite continued flow of a given type. Thetexture development is strongly influenced by temperature, particularlyif the temperature is high enough for recrystallization to take place.

[0076] In general, plastic strains near the surface of a rolled specimenmay differ from those in the interior and may produce textures that varywith depth below the surface. Therefore, specific rolling procedures canhelp ensure reasonably consistent textures throughout the thickness ofthe material. Forward rolling alone may result in homogenous texturethroughout the thickness of the material. For most materials, however,reverse rolling (where the rolling direction is reversed after eachpass) provides a more homogenous texture. Accordingly, reverse rollingcan be used to improve the texture of the material.

[0077] Rolling speed may be an important feature in the texturedevelopment of the material, although its effect is not dominating. Ingeneral, higher rolling speeds are desirable for economical purposes.The lubrication employed during rolling can also be an importantvariable. Depending upon the texture desired, either no lubricant orsome lubricant, such as light mineral oil, heavy mineral oil, orkerosene, can be employed to ensure homogenous texture development.Grain size of the starting material and prior heat treatments anddeformation history can also be important in determining the texturedevelopment. In general, prior to rolling, a fine grain size is desiredand the initial heat treatments and deformations are designed to give arandom texture in the starting material.

[0078] After the material is rolled to the desired texture, it isannealed. The development of an annealing texture involves severalfundamental mechanisms. An annealing texture may develop from recoverywithout recrystallization (in which case it would be expected toduplicate the texture present before annealing), from primaryrecrystallization, or from grain growth subsequent to recrystallization.

[0079] Grain size distribution can remain normal throughout the process,or a few grains may grow very large while the rest remain approximatelyunchanged until devoured by the large ones.

[0080] According to the invention, the metal material can be annealed ina reducing atmosphere to develop biaxial texture. This can beaccomplished by annealing in a vacuum at a predetermined pressure. Thepressure may be any suitable pressure, and is preferably lower thanapproximately 5×10⁻⁶ Torr, and optimally less than approximately 2×10⁻⁶Torr. During vacuum annealing, the metal material is enclosed in anenvelope formed from a material which attracts oxygen, such as tantalum.For Ni and Ni-based alloys, annealing can occur at a temperature rangeof between approximately 600° C. and approximately 1100° C. Preferably,however, annealing occurs between approximately 800° C. andapproximately 1000° C., and ideally occurs at 1000° C. For Cu andCu-based alloys, annealing can occur at a temperature range of betweenapproximately 400° C. and approximately 1000° C.

[0081] Preferably, however, annealing occurs between approximately 500°C. and approximately 900° C. Annealing may continue for any appropriateamount of time, and preferably occurs for approximately 60 minutes.After rolling and annealing, a biaxially-textured metal substrate isformed upon which epitaxial layers may be grown thereon. Although thebiaxially-textured metal substrate can be any metal or metal alloy uponwhich an epitaxial layer may be grown, the metal substrate is preferablycomposed of biaxially-textured Cu, Cu alloy, Co, Mo, Cd, Pd, Pt, Ag, Al,Ni, or Ni alloy. If the metal substrate is a Cu or Ni alloy, any Cu orNi alloy upon which an epitaxial layer can be grown is acceptable.Preferably, the Ni is alloyed with Cr, Mo, V, Co, Cu, or a rare earthelement. These materials are generally preferred for most applicationsbecause they tend to reduce ferromagnetism.

[0082] The starting purity of the metal substrate is preferably at least99.9%, and in a particularly preferred embodiment is greater than99.99%. The degree of biaxial texture in the metal substrate, specifiedby the FWHM of the out-of-plane and in-plane diffraction peak, istypically greater than 2° and less than 20°, preferably less than 15°,and optimally less than 10°.

[0083] An alternative method of forming a biaxially-textured metalsurface is by ion-beam assisted deposition. With this technique, a metalfilm is deposited by a vacuum deposition technique in the presence of anenergetic ion beam. The energetic ions induce a preferredcrystallographic texture in the depositing film. For (001) texturedcubic materials such as Ni, an ion beam directed at an angle ofapproximately 45° or 54° can induce in-plane texture. These anglescorrespond to the (100) and (111) directions of a cube oriented with its(100) direction perpendicular to the metal surface. In this case, themetal surface is preferably composed of Cu, Cu-based alloys, Ni,Ni-based alloys, Ag, Al, Pt, Pd, Cd, Mo, or Co.

[0084] It is understood that, instead of having a biaxial texture, themetal surface can be crystalline with a single uni-axial orientation, orpolycrystalline with arbitrary grain-to-grain orientation, depending onthe intended application. In both cases, the crystallographicorientation of the epitaxial layer will be approximately that of theimmediate metal surface.

[0085] Assuming preparation of a substrate with a textured metalsurface, an epitaxial lanthanum metal oxide layer is grown on thetextured metal surface. For a given buffer, substrate and desiredtop-layer material, there will be some optimum thickness for the bufferlayer. Preferably, the minimum thickness of a buffer layer is determinedby its ability to be chemically compatible with both the substrate andthe top layer material, and to act as a chemical diffusion barrier tocontaminants that would otherwise, “poison” the desired top-layermaterial. For example, nickel is a commonly used substrate materialwhich is known to substantially degrade superconducting properties of asuperconductor if allowed to reach the superconducting layer.

[0086] A buffer layer must also grow epitaxially on the substrate, andto act as a crystalline template for growth of the top layer. If thebuffer layer is too thick, there may be roughening or cracking due tostrain buildup, either due to lattice mismatch or differential thermalexpansion, and the cost of fabrication will increase.

[0087] Applied to superconducting top layers, buffer layers arepreferably at least several tens of nanometers thick (e.g. 50 nm) andpreferably not more than 1 micron thick (1000 nm).

[0088] Any suitable vacuum or non-vacuum deposition process may be usedto grow the lanthanum metal oxide epitaxial layer. Suitable depositionprocesses can include vacuum methods such as pulsed laser deposition,physical vapor deposition, electron beam evaporation, and sputteringnon-vacuum methods such as chemical solution deposition and chemicalvapor deposition. In a preferred embodiment, however, magnetronsputtering is used to deposit the lanthanum metal oxide epitaxial layeron the metal substrate.

[0089] The sputtering process is preferably performed in a vacuum systemwith a base pressure of less than approximately 1×10⁻⁵ Torr, and isoptimally less than approximately 1×10⁻⁶ Torr. The metal surface isheated in the vacuum chamber to a growth temperature which is preferablybetween approximately 200° C. and approximately 900° C., and isoptimally in the range of approximately 500° C. to approximately 700° C.Preferably, an inert sputter gas is used, at a sputter pressure of 1-10mTorr.

[0090] A superconducting layer, such as YBCO can be deposited on thebuffer layer preferably using pulsed laser deposition (PLD). During PLD,the laser energy should be between 1 J/cm² and 10 J/cm². Preferably thelaser energy is between 2.0 J/cm² and 4.0 J/cm². During deposition ofYBCO, substrates are preferably heated to 750° C. to 800° C. inapproximately 120 mTorr of O₂.

EXAMPLES Example 1

[0091] Growth of LSMO on textured-Ni/Ni—W (3%) Substrates by SputteringFollowed by YBCO Deposition

[0092] Biaxially textured Ni (100) substrates were obtained bymechanical deformation of Ni rods to about a 95% reduction in thickness.Mechanical deformation was followed by recrystallization to the desired{100}<001 > cube texture by annealing at 1100° C. for 1-2 hr in ahigh-vacuum furnace with a base pressure of 2×10⁻⁶ Torr. Similarly, Ni—W(3%) substrates with reduced magnetism were produced. The 50 μm thickas-rolled Ni/Ni-alloy substrates were cleaned in isopropanol prior toannealing.

[0093] After annealing, the Ni substrates were mounted on a heater blockusing Ag paint and loaded into the vacuum chamber for on-axissputtering. The annealed Ni—W (3 atomic %) substrates are much strongerand have reduced magnetism compared to pure Ni substrates. The yieldstrength (YS) at 0.2% is 150-200 MPa. This is comparable to 164 MPa YSfor Ni—Cr (13 atomic %) substrates. The La_(0.7)Sr_(0.3)MnO₃ (LSMO)buffer layer depositions were performed with an rf-magnetron sputteringsystem of base pressure 1×10⁻⁶ Torr, using oxide sputter targets thatwere 95 mm in diameter and a power of 67 Watts. Unlike the sintered andhard-pressed CeO₂ and YSZ targets, the LSMO target was made from asingle-phase LSMO powder, which was lightly packed into a copper tray.Deposition of LSMO layer was accomplished by sputtering at substratetemperatures ranging from 550-650° C. in the presence of Argon and/orArgon-H₂ (4%) mixture. Oxygen was not added intentionally. In some runs,water was added into the system to produce stoichiometric LSMO films.The deposition rate was approximately 0.71 Å/sec. The LSMO filmthickness was varied in the range 200-1000 nm to investigate the effecton the microstructure and on the superconducting properties of thesubsequent high temperature superconductor layer. The sputteringpressure was around 3 mTorr. Similar to rf magnetron sputtering, it maybe possible to deposit LSMO buffers layers reactively using dcsputtering. In addition, it is possible to sputter buffers in thepresence of low pO₂,

[0094] A pulsed laser deposition (PLD) technique was employed fordeposition of the YBCO films on the LSMO buffers using a XeCl excimerlaser system, operated with an energy density of approximately 4 J/cm².During deposition of the YBCO films, the substrates were kept at 780° C.in 120 mTorr of O₂. After deposition, the samples were first cooled to600° C. at a rate of 5° C./min, then the O₂ pressure was increased to550 Torr, and the samples cooled to room temperature at the same rate.Typical film thicknesses of YBCO coating were 190 nm.

[0095] The films were analyzed by X-ray diffraction. A Philips modelXRG3100 diffractometer with Cu K_(α) radiation was used to record powderdiffraction patterns. A Picker four-circle diffractometer was used todetermine the texture of the films. SEM micrographs were taken using aJOEL JSM-840 scanning electron microscope, Peabody, Mass., USA. Thethickness of both buffers and YBCO films were determined by bothRutherford backscattering spectroscopy (RBS) and Alpha Step profilometerscans. The resistivity and transport critical current density, J_(c) wasmeasured using a standard four-probe technique. Electrical contacts ofAg were deposited onto the samples using DC sputtering followed by O₂annealing in 1 atm for 30 minutes at 500° C. Values of J_(c) werecalculated using a 1-μV/cm criterion.

[0096]FIGS. 3 and 4 illustrate the presence of a c-axis aligned LSMOfilm on textured-Ni—W (3%) and textured-Ni substrates, respectively.FIG. 5 shows the presence of a single cube textured LSMO film on atextured-Ni substrate. The presence of four-fold symmetry indicates thepresence of a single cube textured LSMO film.

[0097]FIG. 6 shows that crack-free LSMO buffers were produced. FIG. 7shows RBS spectra measured with 5.0 MeV He²⁺ ions at near-normalincidence, detected at a 160° scattering angle. From the RBS spectra inFIG. 7, the simulated LSMO film thickness was determined to be 600 nm.

[0098]FIG. 8 shows the metallic electrical behavior of the LSMO bufferlayer over a range of temperatures. The resistivity behavior of both Niand LSMO buffer layer were substantially the same. The YBCO films onLSMO/Ni substrates had comparable low resistivities at room temperature.The typical room temperature YBCO resistivity is around 250-300 μohm-cm.The observation of very low resistivity of 7 μOhm-cm for YBCO films onLSMO buffered Ni substrates demonstrates that the YBCO is in goodelectrical contact with the bottom Ni substrates through theelectrically conductive LSMO buffer layer. The T_(c) ^(zero) is atapproximately 88.5 K.

[0099] The ω and φ scans for a 190 nm thick PLD YBCO film on 600 nmthick sputtered LSMO/Ni substrates is shown in FIG. 9. The FWHM valuesfor each scan are shown inside the scans in FIG. 9. The FWHM values forboth LSMO buffer and YBCO layers were almost the same as that of the Nisubstrates.

[0100] The YBCO (113) pole figure shown in FIG. 10 indicates thepresence of a single cube textured YBCO film. The field dependence ofcritical current density, J_(c) for a 190 nm thick PLD YBCO film on 600nm thick sputtered LSMO/Ni substrates are shown in FIG. 11. Underself-field, the J_(c) obtained at 77 K is 530,000 A/cm². There is a dropof over 80% in J_(c) in the presence of an H field of 0.5 Tesla.

Example 2

[0101] Growth of LMO (LaMnO₃) on Textured-Ni/Ni—W (3 at. %) Substratesby Sputtering Followed by YBCO Deposition

[0102] Biaxially textured Ni (100) substrates were obtained bymechanical deformation of Ni rods to about a 95% reduction in thickness.Mechanical deformation was followed by recrystallization to the desired{100}<001 > cube texture by annealing at 1100° C. for 1-2 hr in ahigh-vacuum furnace with a base pressure of 2×10⁻⁶ Torr. Similarly, Ni—W(3 at. %) substrates with reduced magnetism were annealed at 1300° C.for 1 hr in a flowing 1 atm Argon-H₂ (4%) gas mixtures. The 50 m thickas-rolled Ni/Ni-alloy substrates were cleaned in isopropanol prior toannealing.

[0103] After annealing, the Ni substrates were mounted on a heater blockusing Ag paint and loaded into the vacuum chamber for on-axissputtering. The annealed Ni—W (3 atomic %) substrates are much strongerand have reduced magnetism compared to pure Ni substrates. The LaMnO₃(LMO) buffer layer depositions were performed with an rf-magnetronsputtering system of base pressure 1×10⁻⁶ Torr, using oxide sputtertargets that were 95 mm in diameter at a power of 67 Watts. The LMOtarget was made from a single-phase LMO powder, which was lightly packedin a copper tray.

[0104] Deposition of LMO layer was accomplished by sputtering atsubstrate temperature ranging from 500-650° C. in the presence of Argonand/or Argon-H₂ (4%) mixture. The deposition rate was approximately 0.6A/sec. The sputtering pressure was around 3 mTorr. Similar to rfmagnetron sputtering, it may be possible to deposit LMO buffer layersreactively using dc sputtering. In addition, it is possible to sputterbuffers in the presence of low pO₂.

[0105] A pulsed laser deposition (PLD) technique was employed fordeposition of the YBCO films on the LMO buffers using a XeCl excimerlaser system, at 790° C. in 120 mTorr of O₂. Typical film thicknesses ofthe YBCO coatings were 200 nm.

[0106] The films were analyzed by detailed X-ray diffraction andtransport property measurements.

[0107]FIG. 12 illustrates a typical θ-2θ scan for a 300 nm thick LMOfilm on {100}<001 > Ni substrates while FIG. 13 illustrates a typical0-20 scan for a 300 nm thick LMO film on {100}<001 > Ni—W (3%)substrates. These demonstrate the presence of a c-axis aligned LMO filmon textured-Ni and Ni—W (3%) substrates, respectively. FIG. 14 is a LMO(111) pole figure for a 300 nm thick sputtered LMO/Ni substrate whichshows the presence of a single cube textured LMO film on a textured-Nisubstrate. The presence of four-fold symmetry indicates the presence ofa single cube textured LMO film.

[0108]FIG. 15 illustrates Omega (ω) and Phi (φ) scans for a 200 nm thickPLD YBCO film on a 300 nm thick sputtered LMO/Ni substrate. The FWHMvalues for each scan are shown inside the scans in FIG. 15. The FWHMvalues for both LMO buffer and YBCO layers were almost the same as thatof the Ni substrates. FIG. 16 illustrates the temperature dependence ofresistivity for a 200 nm thick PLD YBCO film on 300 nm thick sputteredLMO/Ni substrates. The transition temperature, T_(c) (zero resistance)is at 90.4 K. The observation of a higher T_(c) indicates that there isessentially no contamination from the underlying LMO layer. Underself-field, the critical current density, J_(c) obtained at 77 K is320,000 A/cm².

[0109] It should be understood that the examples and embodimentsdescribed herein are for illustrative purposes only and that variousmodifications or changes in light thereof will be suggested to personsskilled in the art and are to be included within the spirit and purviewof this application. The invention can take other specific forms withoutdeparting from the spirit or essential attributes thereof.

We claim:
 1. An epitaxial article, comprising: a substrate having a textured metal surface; a single lanthanum metal oxide epitaxial buffer layer disposed on and in contact with said surface of said substrate, and an electromagnetically active layer disposed on and in contact with said single epitaxial buffer layer.
 2. The article according to claim 1, wherein said lanthanum metal oxide epitaxial buffer layer is selected from compounds having the general formula La_(1-x)A_(x)MO₃, wherein A and M are metals and 0≦x≦0.8.
 3. The article according to claim 2, wherein A is at least one selected from the group consisting of Sr, Ba and Ca.
 4. The article according to claim 2, wherein M is at least one selected from the group consisting of Mn and Co.
 5. The article according to claim 1, wherein said lanthanum metal oxide epitaxial buffer layer has a resistivity at 300 K of less than 1 mOhm-cm.
 6. The article according to claim 1, wherein said lanthanum metal oxide epitaxial buffer layer has a resistivity at 300 K of less than 0.1 mOhm-cm.
 7. The article according to claim 1, wherein said electromagnetically active layer includes a superconducting layer.
 8. The article according to claim 7, wherein said superconductor layer comprises an oxide superconductor.
 9. The article according to claim 7, wherein said oxide superconductor comprises at least one oxide superconductor selected from the group consisting of REBa₂Cu₃O₇ where RE is a rare earth element, Tl₁Ba₂Ca_(n−1)Cu_(n)O_(2n+3), where n is an integer between 1 and 4, Tl₂Ba₂Ca_(n−1)Cu_(n)O_(2n+4) where n is an integer between 1 and 4, and Hg₁Ba₂Ca_(n−1)Cu_(n)O_(2n+2), where n is an integer between 1 and
 4. 10. The article according to claim 1, wherein said substrate is a rolled and annealed biaxially-textured metal substrate.
 11. The article according to claim 1, wherein said textured metal surface comprises at least one metal selected from the group consisting of Cu, Cu-based alloys, Co, Mo, Cd, Pd, Pt, Ag, Al, Ni, and Ni-based alloys.
 12. The article according to claim 1, wherein said textured metal surface comprises at least one metal selected from the group consisting of Ni and Ni-based alloys with at least one alloying agent selected from the group consisting of Co, Cr, V, Mo, W, and rare earth elements.
 13. An epitaxial article, comprising: a substrate having a textured metal surface; a lanthanum metal oxide epitaxial buffer layer disposed on and in contact with said surface of said substrate; at least one epitaxial capping layer disposed on and in contact with said lanthanum metal oxide epitaxial buffer layer, said epitaxial capping layer being of a different composition than said lanthanum metal oxide epitaxial buffer layer, and an electromagnetically active layer disposed on and in contact with said epitaxial capping layer.
 14. The article according to claim 13, wherein said epitaxial buffer layer is selected from compounds having the general formula La_(1-x)A_(x)MO₃, wherein A and M are metals and 0≦x≦0.8.
 15. The article according to claim 14, wherein A is at least one selected from the group consisting of Sr, Ba and Ca.
 16. The article according to claim 14, wherein M is at least one selected from the group consisting of Mn and Co.
 17. The article according to claim 15, wherein said electromagnetically active layer includes a superconducting layer.
 18. The article according to claim 17, wherein said superconductor layer comprises an oxide superconductor.
 19. The article according to claim 17, wherein said oxide superconductor comprises at least one oxide superconductor selected from the group consisting of REBa₂Cu₃O₇, where RE is a rare earth element Tl₁Ba₂Ca_(n−1)Cu_(n)O_(2n+3), where n is an integer between 1 and 4, Tl₂Ba₂Ca_(n−1)Cu_(n)O_(2n+4), where n is an integer between 1 and 4, and Hg₁Ba₂Ca_(n−1)Cu_(n)O_(2n+2), where n is an integer between 1 and
 4. 20. The article according to claim 13, wherein said substrate is a rolled and annealed biaxially-textured metal substrate.
 21. The article according to claim 13, wherein said metal textured surface comprises at least one metal selected from the group consisting of Cu, Cu-based alloys, Co, Mo, Cd, Pd, Pt, Ag, Al, Ni, and Ni-based alloys.
 22. The article according to claim 13, wherein said textured metal surface comprises at least one metal selected from the group consisting of Ni and Ni-based alloys with at least one alloying agent selected from the group consisting of Co, Cr, V, Mo, W, and rare earth elements.
 23. The article according to claim 13, wherein said epitaxial capping layer comprises at least one material which is a rare earth oxide.
 24. The article according to claim 13, wherein said epitaxial capping layer is at least one material selected from the group consisting of SRO, LNO, YSZ, CeO₂ and Y₂O₃.
 25. A method for preparing an epitaxial article, comprising the steps of: providing a substrate with a textured metal surface; depositing a single lanthanum metal oxide epitaxial buffer layer on and in contact with said surface of said substrate, and depositing an electromagnetically active layer on and in contact with said single lanthanum metal oxide epitaxial buffer layer.
 26. The method according to claim 25, further comprising the step of providing a biaxially-textured metal surface.
 27. The method according to claim 26, further comprising the step of rolling and annealing a metal material to form said biaxially-textured substrate surface.
 28. The method according to claim 25, further comprising the step of rolling and annealing a metal substrate, said metal substrate comprising at least one metal selected from the group consisting of Cu, Cu-based alloy, Co, Mo, Cd, Pd, Pt, Ag, Al, Ni, and Ni-based alloys.
 29. The method according to claim 25, further comprising the step of rolling and annealing a metal substrate, said metal substrate comprising at least one metal selected from the group consisting of Ni and Ni-based alloy with at least one alloying agent selected from the group consisting of Co, Cr, V, Mo, W, and rare earth elements.
 30. The method according to claim 25, wherein said lanthanum metal oxide epitaxial buffer layer is selected from compounds having the general formula La_(1-x)A_(x)MO₃, wherein A and M are metals and 0≦x≦0.8.
 31. The method according to claim 30, wherein A is at least one selected from the group consisting of Sr, Ba and Ca.
 32. The method according to claim 30, wherein M is at least one selected from the group consisting of Mn and Co.
 33. The article according to claim 25, wherein said lanthanum metal oxide epitaxial buffer layer has a resistivity at 300 K of less than 1 mOhm-cm.
 34. The article according to claim 25, wherein said lanthanum metal oxide epitaxial buffer layer has a resistivity at 300 K of less than 0.1 mOhm-cm.
 35. The method according to claim 25, wherein said electromagnetically active layer includes a superconducting layer.
 36. The method according to claim 35, wherein superconductor layer comprises an oxide superconductor.
 37. The method according to claim 36, wherein said oxide superconductor comprises at least one oxide superconductor selected from the group consisting of REBa₂Cu₃O₇, where RE is a rare earth element, Tl₁Ba₂Ca_(n−1)Cu_(n)O_(2n+3), where n is an integer between 1 and 4; Tl₂Ba₂Ca_(n−1)Cu_(n)O_(2n+4), where n is an integer between 1 and 4, and Hg₁Ba₂Ca_(n−1)Cu_(n)O_(2n+2), where n is an integer between 1 and
 4. 38. The method according to claim 25, wherein said lanthanum metal oxide epitaxial buffer layer is deposited by a sputtering process.
 39. The method according to claim 38, wherein said sputtering process comprises rf-magnetron sputtering.
 40. The method according to claim 25, wherein said electromagnetically active layer is deposited by a process comprising pulsed laser ablation.
 41. A method for preparing an epitaxial article, comprising the steps of: providing a substrate with a textured metal surface; depositing a single lanthanum metal oxide epitaxial buffer layer on and in contact with said surface of said substrate; depositing at least one epitaxial capping layer on said single lanthanum metal oxide epitaxial buffer layer, said epitaxial capping layer being of a different composition than said single lanthanum metal oxide epitaxial buffer layer, and depositing a electromagnetically active layer on said epitaxial capping layer.
 42. The method according to claim 41, further comprising the step of providing a biaxially-textured metal surface.
 43. The method according to claim 42, further comprising the step of rolling and annealing a metal material to form said biaxially-textured substrate.
 44. The method according to claim 41, further comprising the step of rolling and annealing a metal substrate, said metal substrate comprising at least one metal selected from the group consisting of Cu, Cu-based alloy, Co, Mo, Cd, Pd, Pt, Ag, Al, Ni, and Ni-based alloys.
 45. The method according to claim 41, further comprising the step of rolling and annealing a metal substrate, said metal substrate comprising at least one metal selected from the group consisting of Ni and Ni-based alloy with at least one alloying agent selected from the group consisting of Co, Cr, V, Mo, W, and rare earth elements.
 46. The method according to claim 41, wherein said lanthanum metal oxide epitaxial buffer layer is selected from compounds having the general formula La_(1-x)A_(x)MO₃, where A and M are metals and 0≦x≦0.8.
 47. The method according to claim 46, wherein A is at least one selected from the group consisting of Sr, Ba and Ca.
 48. The method according to claim 46, wherein M is at least one selected from the group consisting of Mn and Co.
 49. The method according to claim 41, wherein said electromagnetically active layer includes a superconducting layer.
 50. The method according to claim 49, wherein superconductor layer comprises an oxide superconductor.
 51. The method according to claim 50, wherein said oxide superconductor layer comprises at least one oxide superconductor selected from the group consisting of REBa₂Cu₃O₇, where RE is a rare earth element, Tl₁Ba₂Ca_(n−1)Cu_(n)O_(2n+3), where n is an integer between 1 and 4, Tl₂Ba₂Ca_(n−1)Cu_(n)O_(2n+4), where n is an integer between 1 and 4 and Hg₁Ba₂Ca¹⁻¹Cu_(n)O_(2n+2), where n is an integer between 1 and
 4. 52. The method according to claim 41, wherein said lanthanum metal oxide epitaxial buffer layer is deposited by a sputtering process.
 53. The method according to claim 52, wherein said sputtering process comprises rf-magnetron sputtering.
 54. The method according to claim 41, wherein said electromagnetically active layer is deposited by a process comprising pulsed laser ablation.
 55. The method according to claim 41, wherein said epitaxial capping layer comprises at least one material selected from the group consisting of SRO, LNO, YSZ, CeO₂ and Y₂O₃ and rare earth oxides.
 56. An epitaxial article for providing a foundation for applying electromagnetically active layers directly thereon, comprising: a substrate having a textured metal surface, and a single lanthanum metal oxide epitaxial buffer layer disposed on and in contact with said surface of said substrate, whereby another buffer layer is not required.
 57. The article according to claim 56, wherein said lanthanum metal oxide epitaxial buffer layer is selected from compounds having the general formula where La_(1-x)A_(x)MO₃, wherein A and M are metals and 0≦x≦0.8.
 58. The article according to claim 57, wherein A is at least one selected from the group consisting of Sr, Ba and Ca.
 59. The article according to claim 57, wherein M is at least one selected from the group consisting of Mn and Co.
 60. A method for preparing an epitaxial article for applying electromagnetically active layers directly thereon, comprising the steps of: providing a substrate with a textured metal surface, and depositing a single lanthanum metal oxide epitaxial layer on said substrate.
 61. The method according to claim 60, wherein said metal surface is a biaxially-textured metal surface.
 62. The method according to claim 60, further comprising the step of rolling and annealing a metal material to form a biaxially-textured substrate having a surface.
 63. The method according to claim 60, further comprising the step of rolling and annealing at least one metal selected from the group consisting of Cu, Cu-based alloys, Ag, Al, Co, Mo, Cd, Pd, Pt, Ni, and Ni-based alloys.
 64. The method according to claim 60, further comprising the step of rolling and annealing at least one metal selected from the group consisting of Ni and Ni-based alloy with at least one alloying agent selected from the group consisting of Co, Cr, V, Mo, W, and rare earth elements.
 65. The method according to claim 60, wherein said lanthanum metal oxide epitaxial layer is selected from compounds having the general formula La_(1-x)A_(x)MO₃, herein A and M are metals and 0≦x≦0.8.
 66. The method according to claim 60, wherein said lanthanum metal oxide epitaxial layer is deposited using a sputtering process.
 67. The method according to claim 66, wherein said sputtering comprises rf-magnetron sputtering.
 68. An epitaxial article, comprising: a substrate having a metal surface; a single electrically conductive epitaxial buffer layer disposed on and in contact with said surface of said substrate, and an electromagnetically active layer disposed on and in contact with said single epitaxial buffer layer, said epitaxial buffer layer being substantially crack-free.
 69. The article according to claim 68, wherein said epitaxial buffer layer is at least 100 nm thick.
 70. The article according to claim 68, wherein said epitaxial buffer layer has a resistivity at 300 K of less than 1 mOhm-cm.
 71. The article according to claim 68, wherein said epitaxial buffer layer has a resistivity at 300 K of less than 0.1 mOhm-cm.
 72. The article according to claim 68, wherein said electromagnetically active layer includes a superconducting layer. 